The present invention relates generally to apparatuses having rotary members, and more particularly to an apparatus having a rotary member to which a flexible printed circuit board is attached. The present invention can be applied to a head actuator of a magnetic disk drive, an analog meter and the like.
A magnetic disk drive shown in FIG.1 is an example of a conventional apparatus to which a flexible printed circuit board (called FPC for short) is attached. A head actuator 1 is a rotary type actuator, and is mounted pivotably around a shaft 2. The actuator 1 comprises a head arm 4 which has a magnetic head 3 at the top thereof. The actuator 1 pivots around the shaft 2, and moves the head 3 in an approximately radial direction (direction A) of a magnetic disk 5 when a voice coil motor having a driving coil 1a is electrified. The head 3 is positioned at a predetermined track according to the current strength supplied to the voice coil motor and the like. Information which is recorded on the disk 5 and/or reproduced therefrom by the head 3, the electricity supplied to the voice coil motor and the like are transmitted between the magnetic disk drive and an external device (not shown) via the FPC 7 and a printed circuit board 6. The FPC 7 is connected to an attachment portion lb of the actuator 1 at an end 7a thereof, which portion does not block a moving locus of the head 3, and is connected to the printed circuit board 6 at the other end 7b thereof.
However, the conventional magnetic disk drive has the following disadvantages. The actuator 1 is subjected to a force F.sub.1 at the attachment portion 1b in a direction vertical to the tangential direction of the FPC 7 at the end 7a thereof and a force F.sub.2 in a direction parallel to the tangential direction. The actuator 1 can rotate within a range of approximately 20.degree. angles, and within this range, the force F.sub.1 influences the actuator 1 more negatively than the force F.sub.2.
Therefore:
1. The actuator 1 is subjected to a moment M, counterclockwise around the shaft 2, mainly generated by the force F.sub.1, so it is difficult to position the head 3 over the disk 5 precisely;
2. The voice coil motor needs more electricity because the head 3 is positioned against the moment M;
On the other hand, the strength of the force F.sub.1 is proportional to the length of a radius R of a bent portion of the FPC 7. The smaller the radius R is, the larger the force F.sub.1 (and the moment M) is, while the larger the radius R is, the smaller the force F.sub.1 is. The radius R depends upon the rotating of the actuator 1, thus the radius R is largest when the head 3 is at the most inner track of the disk 5, and is smallest when the head 3 is at the most outer track. Therefore the moment M changes depending on the rotating of the actuator 1. Accordingly, when considering the positions of a first track and a second track which is located at a more inner position than the first track, it will be seen that the head 3 spends an amount of time moving from the first track to the second track different from the amount of time spent moving from the second track to the first track. Consequently:
3. The time for moving the head 3 to the predetermined track of the disk 5 (the seek time) cannot be made uniform;
To solve the above problem, it would be conceivable, as shown in FIG.2, to use a long FPC 8 in order to enlarge the radius R. But such a solution includes the following disadvantages. The magnetic disk drive is subjected to noises caused by an external magnetic field. In addition, the longer the FPC 8 is, the longer is a part of the FPC 8 which is crossed with the external magnetic field. Therefore:
4. Recorded and/or reproduced information involves more noise; and
5. The longer FPC is extremely expensive.
Even if the FPC is applied to an analog meter, the analog meter would include disadvantages similar to the above ones.